The present disclosure relates to an image forming apparatus that uses induction heating to fix toner to a sheet.
Some of the image forming apparatuses such as a multifunctional peripheral, a copying machine, a printer and a facsimile machine use toner to perform image formation. In such an image forming apparatus, a toner image is transferred to a sheet while the sheet is being transported therewithin, and heating and pressurizing are performed to fix the toner image to the sheet. In some of the image forming apparatuses that fix the toner to perform printing, an induction heating method is used to perform the fixing.
A fixing control device that uses the following induction heating method to perform fixing is known. Specifically, the fixing control device includes: a main body control circuit that has a main central processing unit controlling the operation of the entire device; a temperature sensor that detects the temperature of a fixing heated member; an exciting coil for inductively heating the fixing heated member by receiving current supply; and an induction heating control circuit that has a sub-central processing unit independent of the main central processing unit to control the current supply to the exciting coil, where based on information on the temperature detected by the temperature sensor, the main central processing unit uses only a power instruction signal to provide a control instruction to the sub-central processing unit.
In the image forming apparatus of the induction heating method, as in the fixing control device described above, a plurality of control portions may be provided, and the roles of the induction heating are allocated. Specifically, a main control portion that controls the image forming apparatus is made to provide an instruction of power to be supplied to the exciting coil based on the temperature of a heating rotation member. The control portion provided in a fixing portion may be made to perform actual control for supplying power on the exciting coil based on an instruction from the main control portion.
On the other hand, in order for a fixing failure and overheating in the fixing portion to be prevented, the detection of a temperature abnormality in the heating rotation member based on the output from the temperature sensor is performed. The detection of an abnormality in a voltage or a current, that is, power supplied to the exciting coil may be performed. When a temperature abnormality or a power abnormality is detected, the stop of a printing operation and/or the stop of power supply to the exciting coil is performed. Thus, printing and power supply in an inappropriate state are prevented.
Conventionally, when such an abnormality occurs in the fixing portion, in the image forming apparatus, notification of the abnormality is provided. For example, on the display portion of the image forming apparatus, information that an abnormality is produced in the fixing portion or information that checking or repair is needed is displayed.
Here, the temperature abnormality in which the temperature of the heating rotation member of the fixing portion is lower than a temperature to be detected may be caused by the stop of the power supply to the exciting coil resulting from an abnormality in supply power or may be caused by an abnormality in the temperature sensor. However, conventionally, when the temperature abnormality is produced, notification is not provided for each cause. Hence, although there is a problem in a power supply system that supplies power to the exciting coil, a service person may erroneously determine that the cause is present in the temperature sensor. On the contrary, although the cause is preset in the temperature sensor, a service person may erroneously determine that there is a problem in the power supply system that supplies power to the exciting coil. As described above, when a temperature abnormality is produced in the fixing portion, it is disadvantageously difficult to determine the cause of the abnormality.
A fixing device controlled by the known fixing control device described above performs induction heating. However, it is impossible to solve the problem in which it is difficult to determine the cause of the temperature abnormality produced in the fixing portion.